Sprayable Acoustic Compositions

ABSTRACT

The invention relates to sprayable acoustic compositions, production processes and uses.

The invention relates to sprayable acoustic compositions, production processes and uses.

Surfaces set in vibration emit sound. This can be highly desirable, for example in the case of musical instruments; however, it can also be regarded as problematic, especially if this sound is perceived as noise.

By way of example, sheet metal in the bodywork of automobiles is excited via the engine, the road surface or stone impact to produce vibrations which are perceived as rumble in the interior of the vehicle.

In order to damp these undesired sheet metal vibrations, the automobile industry often applies bitumen mats to the sheet metal. Although this is a successful method of sound-deadening for the interior, it has at the same time a large number of disadvantages.

A stock of the bitumen mats trimmed to size in the correct shape has to be held for every surface; when a plurality of shapes of mat have to be provided for various vehicle models this represents a challenge in terms of logistics and stock management.

Manual labour is used to apply the mats by adhesive bonding, and this is naturally a cause of quality variations.

Furthermore, there are some toxicological reservations about bitumen.

Sprayable or extrudable compositions have been discussed for some years as replacement for these bitumen mats, and in many respects are superior to the bitumen mats.

These compositions applied by robots can be applied even to complex-shaped or curved sheet metal without difficulty.

It is very easy to make adjustments for altered requirements or change of model.

Automation can achieve a reduction in the amount of manual labour and an improvement in process quality.

Compositions of this kind have been previously described and are to some extent also now used in small quantities in automobile production. However, materials of this type have not yet achieved a breakthrough, since all of the systems proposed hitherto have disadvantages which inhibit their adoption.

Firstly, materials based on PVC or on chlorinated thermoplastics have been proposed, for example in the form of plastisol in EP 0456473 or EP 766714, or in the form of a composition requiring hot processing in EP 1277823. However, chlorine-containing plastics are disadvantageous for environmental reasons, since they can form HCl and highly toxic dioxins on incineration, and this also has attendant disadvantages especially during recycling. In the case of the compositions disclosed in EP 1277823, another disadvantage is the need for hot processing.

Aqueous dispersions have moreover been described, which on drying give a film having the desired damping property; materials of this type are described by way of example in the publications EP 1457530 and EP 1520865. Specifically in the case of relatively thick layers such as those needed for good damping action, however, these materials require long drying times in order to remove the water from the sprayed-on layer. Associated with this there is the risk of undesired formation of bubbles, especially if the drying procedure is accelerated.

Compositions based on epoxy resins have likewise been widely proposed; examples are provided by the publications EP 0407157, EP 1023413 and EP 1500690. However, there are some reservations about the constituents of these resins, and they are often allergenic or even mutagenic and carcinogenic. Since these coatings are often very hard and brittle they are mostly unsuitable for external use. Repair in the event of damage is also very difficult with this material.

Finally, plasticizers have also been described with binders based on (meth)acrylate, for example in EP 0702708 or in EP 1090067.

The term (meth)acrylate here and hereinafter means not only the esters of methacrylic acid but also the esters of acrylic acid, and also mixtures of the two. Examples of these monomers are methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, ethyl acrylate and butyl acrylate.

The term (meth)acrylate plastisols is used hereinafter to describe plastisols whose polymeric constituents are composed to a substantial extent of (meth)acrylates.

However, these (meth)acrylate plastisols require very high contents of plasticizers in order to ensure sufficient processibility. These can evaporate to a limited extent out of the coating, especially in new vehicles. If these plastisols are used in vehicle interiors, this leads to an increased level of fogging, i.e. deposition of these vapours on the windowpanes of the vehicle. Fogging is undesired and problematic, since it impairs the view through the windowpanes, especially in sunlight or other types of glare.

The object therefore consisted in providing a material for vibration damping which excludes all of the disadvantages revealed in the prior art. The object also consisted in improvement of existing plastisol materials. The intention is to provide plastisols which comprise less volatile constituents, these being responsible for fogging.

These objects, and also other objects which, although not explicitly stated, are readily deducible or derivable from the circumstances discussed in the introduction to this specification, are achieved via a formulation, comprising

-   a) from 1 to 60% by weight of oligomers whose molar mass is smaller     than 20 000 g/mol, -   b) from 0 to 60% by weight of solvents for the oligomers a), -   c) from 5 to 60% by weight of pulverulent polymers whose molar mass     is greater than 100 000 g/mol, and -   d) other fillers, auxiliaries and/or additives, where components a)     to c) make up at least 20% of the formulation. Components a) to c)     preferably make up 40% of the formulation.

It has been possible to reduce fogging via replacement of the entire amount, or of a part, of the plasticizer usually used in plastisols by oligomers, in particular (meth)acrylate oligomers.

The inventive formulations have excellent processibility.

Surprisingly, it has also been found possible to observe a marked improvement in the damping properties of the coating.

The use of (meth)acrylate plastisols meets the requirement of flexibility in dealing with various surface shapes and curvatures; another result is optimized stock management of the damping materials.

The oligomers a) encompass monomer constitutions which can not only be composed of various types of monomer but can also comprise various chain lengths corresponding to the distribution curves.

The molar mass M_(w) of the oligomers a) is <20 000 g/mol, preferably <10 000 g/mol, particularly preferably <5000 g/mol, and they preferably contain at least 30% by weight of (meth)acrylates, particularly preferably at least 60% by weight of (meth)acrylates.

The oligomers a) have preferably been selected from the group of the (meth)acrylates, such as alkyl (meth)acrylates of straight-chain, branched, or cycloaliphatic alcohols having from 1 to 22 carbon atoms, examples being methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, aryl (meth)acrylates, such as benzyl (meth)acrylate or phenyl (meth)acrylate, each of which can be unsubstituted or can have mono- to tetra-substituted aryl radicals, mono(meth)acrylates of ethers, of polyethylene glycols, of polypropylene glycols, or their mixtures having from 5 to 80 carbon atoms, e.g. tetrahydrofurfuryl methacrylate, methoxy(m)ethoxyethyl methacrylate, 1-butoxypropyl methacrylate, cyclohexyloxymethyl methacrylate, benzyloxymethyl methacrylate, furfuryl methacrylate, 2-butoxyethyl methacrylate, 2-ethoxyethyl methacrylate, allyloxymethyl methacrylate, 1-ethoxybutyl methacrylate, 1-ethoxyethyl methacrylate, ethoxymethyl methacrylate, poly(ethylene glycol) methyl ether (meth)acrylate, poly(propylene glycol)methyl ether (meth)acrylate, styrene, and substituted styrenes, e.g. 4-vinylbenzoic acid.

The inventive oligomers have to have no reactive groups of any kind, because their role in the processible form of the formulation is that of a solvent and their role in the fully gelled form is that of a binder.

However, it can be advantageous in specific embodiments to modify the physical properties of the oligomers, such as the properties of hydrophilicity or of polarity, via incorporation of additional functional groups; examples which may be mentioned are hydroxy groups (e.g. via the use of hydroxyethyl methacrylate or hydroxypropyl methacrylate as comonomer), acid groups (e.g. via the use of acrylic acid or methacrylic acid or hydroxypropyl methacrylate as comonomer) or amide groups (e.g. via the use of acrylamide or methacrylamide as comonomer).

Processes known to the person skilled in the art are used to synthesize the oligomers. They are generally prepared via solution polymerization using chain transfer agents; typical chain transfer agents are sulphur compounds, such as mercaptans (e.g. 1-dodecanethiol, 1-butanethiol, etc.). For certain monomers it is also possible to use catalytic chain transfer agents; examples of these CCT catalysts are cobalt(II) complexes with porphyrin ligands or with glyoximine ligands (e.g. 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphyrin-cobalt (II), 2,3,7,8,12,13,17,18-octa-ethyl-21H,23H-porphyrincobalt (II), bis[(difluoroboryl)diphenylglyoxime]cobalt(II) or bis[(difluoroboryl)diphenylglyoxime] cobalt (II)). In the cases where this is possible the use of catalytic chain-transfer agents is particularly preferred.

The formulation can be prepared either with solvents or else without solvents. Solvents that can be used are liquids or mixtures of liquids which in the binary mixture with the respective oligomers in the quantitative proportioning intended in the respective formulation form an optically clear solution which exhibits no separation or phase formation even after 24 hours of standing at 20° C.

Less preference is given to liquids which in this mixture with the oligomers exhibit clouding immediately or within 24 hours, but without any settling or creaming of any of the components, but they can nevertheless be used in specific embodiments.

Particular mention may be made of the following solvents, but the list can be extended as desired and is not to be understood as limiting:

esters of phthalic acid, e.g. diundecyl phthalate, diisodecyl phthalate, diisononyl phthalate, dioctyl phthalate, diethylhexyl phthalate, di-C7-C11-n-alkyl phthalate, dibutyl phthalate, diisobutyl phthalate, dicyclohexyl phthalate, dimethyl phthalate, diethyl phthalate, benzyl octyl phthalate, butyl benzyl phthalate, dibenzyl phthalate, and tricresyl phosphate, dihexyldicapryl phthalate.

Hydroxycarboxylic esters, e.g. esters of citric acid (for example tributyl O-acetylcitrate, triethyl O-acetylcitrate), esters of tartaric acid or esters of lactic acid.

Aliphatic dicarboxylic esters, e.g. esters of adipic acid (for example dioctyl adipate, diisodecyl adipate), esters of sebacic acid (for example dibutyl sebacate, dioctyl sebacate, bis(2-ethylhexyl) sebacate) or esters of azelaic acid.

Esters of trimellitic acid, e.g. tris(2-ethylhexyl) trimellitate. Esters of benzoic acid, e.g. benzyl benzoate.

Esters of phosphoric acid, e.g. tricresyl phosphate, triphenyl phosphate, diphenyl cresyl phosphate, diphenyl octyl phosphate, tris(2-ethylhexyl) phosphate, tris(2-butoxyethyl) phosphate.

Alkylsulphonic esters of phenol or of cresol, dibenzyltoluene, diphenyl ether.

Preference is given to use of phthalates, adipates, phosphates or citrates; particular preference is given to phthalates.

Use of volatile solvents, such as low-boiling hydrocarbons or their mixtures (e.g. petroleum ether) is less preferred but also certainly advisable in specific embodiments. Use of volatile solvents is targeted particularly at exterior applications, for example in underbody protection, where fogging is not relevant.

The solvents mentioned and other solvents can also be used in the form of mixtures.

The molar mass of the polymers c) is usually >100 000 g/mol, preferably >400 000 g/mol. These polymers can by any of the processes known to the person skilled in the art (e.g. free-radical polymerization, anionic polymerization, cationic polymerization, polyaddition or polycondensation). Free-radical polymerization is preferred.

Accordingly, it is possible to use monomers—or else monomers in mixtures—accessible to any of these polymerization reactions. Preference is given to ethylenically unsaturated compounds, e.g. (meth)acrylates, styrene and its derivatives, unbranched or branched alkenes, vinyl esters and other compounds. (Meth)acrylates are particularly preferred.

It is preferable to use compounds selected from the group of the methyl (meth)acrylates, ethyl (meth)acrylates, propyl (meth)acrylates, isopropyl (meth)acrylates, n-butyl (meth)acrylates, isobutyl (meth)acrylates, tert-butyl (meth)acrylates, 2-ethylhexyl (meth)acrylates, hexyl (meth)acrylates, cyclohexyl (meth)acrylates, pentyl (meth)acrylates, heptyl (meth)acrylates, octyl (meth)acrylates, 1,4-butanediol (meth)acrylates, 2-butoxyethyl (meth)acrylates, 2-ethoxyethoxymethyl (meth)acrylates, 2-ethoxyethyl (meth)acrylates, tetrahydrofurfuryl (meth)acrylates, vinyloxyethoxyethyl (meth)acrylates, methoxyethoxyethyl (meth)acrylates, 1-butoxypropyl (meth)acrylates, 1-methyl-(2-vinyloxy)ethyl (meth)acrylates, cyclohexyloxymethyl (meth)acrylates, methoxymethoxyethyl (meth)acrylates, benzoyloxymethyl (meth)acrylates, furfuryl (meth)acrylates, 2-butoxyethyl (meth)acrylates, 2-ethoxyethoxymethyl (meth)acrylates, β-carboxyethyl acrylates, 2-ethoxyethyl (meth)acrylates, allyloxymethyl (meth)acrylates, 1-ethoxybutyl (meth)acrylates, methoxymethyl (meth)acrylates, 1-ethoxyethyl (meth)acrylates, ethoxymethyl (meth)acrylates, 2,3-epoxybutyl (meth)acrylates, 3,4-epoxybutyl (meth)acrylates, glycidyl (meth)acrylates, 2-(dimethylphosphato)propyl (meth)acrylates, 2-(ethylenephosphito)propyl (meth)acrylates, dimethylphosphinomethyl (meth)acrylates, dimethylphosphonoethyl (meth)acrylates, diethyl methacryloylphosphonates, dipropyl methacryloylphosphates, ethylsulphinylethyl (meth)acrylates, 4-thiocyanatobutyl (meth)acrylates, ethylsulphonylethyl (meth)acrylates, thiocyanatomethyl (meth)acrylates, methylsulphinylmethyl (meth)acrylates, bis(methacryloyloxyethyl) sulphides, trimethyloylpropane tri(meth)acrylates, 1-hexenes, 1-heptenes, cyclohexenes, vinylcyclohexanes, 3,3-dimethylpropenes, 3-methyl-1-diisobutylenes, 4-methyl-1-pentenes, vinyl acetates, styrenes, α-methylstyrenes, α-ethylstyrenes, vinyltoluenes, p-methylstyrenes, esters or diesters of maleic acid, 9-vinylcarbazoles, 3-vinylcarbazoles, 4-vinylcarbazoles, vinyloxolanes, vinylfurans, vinylthiophenes, vinylthiolanes.

It is preferable that at least one of the polymers c) is composed of more than 60% by weight, particularly preferably more than 80% by weight, of (meth)acrylates. In one particular embodiment, each of the polymers c) is composed of more than 60% by weight, preferably more than 80% by weight, of (meth)acrylates.

In another preferred embodiment, at least one of the polymers c) is composed of more than 60% by weight, particularly preferably more than 80% by weight, of methyl methacrylate.

The polymers c) are usually composed of more than 60% by weight of (meth)acrylates.

For good further processibility, an oligomer a) and/or a polymer c) can bear one or more functional groups which can give post-crosslinking. Examples of functional groups that can be used are hydroxy, mercapto, amino, carboxy, carbonyl, sulphonyl, epoxy, β-ketoester and isocyanate groups.

These can, if appropriate, also be present in protected form, e.g. the isocyanate group reacted with, for example, alcohols, with phenols, with oximes, with caprolactams, with amines or with C—H-acidic compounds.

Hydroxy groups are preferred.

The polymers can be prepared via emulsion polymerization, suspension polymerization, solution polymerization or bulk polymerization. Preparation via emulsion polymerization is preferred.

In the case of preparation via emulsion polymerization, the polymers are produced in the form of polymer particles dispersed in water. These have to be converted to a dry powder; the usual methods are suitable for this purpose, examples being coagulation, spray drying and freeze drying. Spray drying is preferred.

The preferred preparation process by means of emulsion polymerization and spray drying gives powder particles whose average particle diameter is usually from 1 to 500 μm, these being composed of individual polymer particles whose average particle diameter is usually from 200 to 1200 nm. Powders of this type are particularly suitable for preparation of the inventive formulations.

(Unless otherwise stated, “average particle diameter” here and hereinafter means the volume-average of the particle size distribution of the specimen. These values can be measured by way of example via laser diffraction, e.g. with the aid of a Coulter LS 13 320 manufactured by Beckmann-Coulter.)

An emulsion polymerization procedure known to the person skilled in the art can also prepare polymer particles which have a core and have one or more shells around the core, and all of the polymers here which form the core and, respectively, form each of the shells can have different monomeric constitutions (core/shell particles).

A similar method can also be used to prepare particles whose monomeric constitution changes continuously from the centre of the particle to its surface, corresponding in some ways to a core-shell particle with very many shells. In this case another term used is particles with gradient morphology or “gradient latices”.

As is well known, polymers and oligomers are practically always composed of mixtures of various molecules, their properties having a distribution around one or more maxima. An example of these properties is molecular weight, which is characterized via average values, the molecular weights of the individual polymer molecules having a distribution—of varying breadth and also sometimes polymodal—around this average value.

Another example relates to chemical constitution. For example, copolymers (specifically in free-radical polymerization) are mostly produced via random incorporation of the available monomers. If, by way of example, a certain monomer A has 2% presence in a monomer mixture its rate of incorporation into an oligomer which is composed of an average of 50 monomer units is statistically once per oligomer. In fact, oligomers without this monomer A will be found, as will oligomers having 2 or 3 of this type of monomer unit, than if oligomers having exactly one incorporated monomer A form the majority.

The intention here is to make it expressly clear that when polymers and oligomers are used materials used are always in a certain sense mixtures, but are not usually perceived and specified as such. (For better comprehensibility and for demarcation, these “inevitable” mixtures are termed polymer material and, respectively, oligomer material in the description hereinafter).

However, the expressions “polymers” and “oligomers” in this specification moreover expressly mean mixtures of a plurality of polymer materials or of a plurality of oligomer materials: by way of example, two or more separately prepared materials with different molecular weight distributions or with different monomer constitutions can be mixed. Materials used as polymers and, respectively, oligomers can moreover also comprise those mixed after they have been obtained by different preparation processes (e.g. an emulsion polymer and a suspension polymer).

Polymer particles which have core-shell or gradient morphology and which have been prepared via emulsion polymerization are moreover also mixtures of different polymer materials, since this structure is specifically manifested via different materials.

The possibility not only of adjusting the properties of individual polymer materials or oligomer materials as desired but also of mixing different materials permitting a targeted approach to all of the requirements of any specific application.

The usual fillers, auxiliaries and/or additives can be added to the formulation.

Commonly used fillers are inter alia calcium carbonate (in various versions, e.g. naturally occurring or precipitated, surface-treated, etc.), barium sulphate (baryte) and silicates, e.g. mica, bentonites, montmorillonite, talc or vermiculite. Barium sulphate is particularly preferred.

Among the auxiliaries and additives are colour pigments, antioxidants, rheology additives, blowing agents and other materials.

Blowing agents are added to the formulations particularly for the foaming of plastisols. Examples of commonly used blowing agents are azo compounds (e.g. azodicarbamide), N-nitroso compounds (e.g. dinitrosopentamethylenetetramine), sulphonyl hydrazides (e.g. 4,4′-oxybis(benzenesulphonic hydrazide)) or sulphonylsemicarbazides (p-toluenesulphonylsemicarbazides).

Carbon blacks are often used as colour pigment.

If appropriate, auxiliaries for post-crosslinking can also be added. These auxiliaries are generally compounds having two or more functional groups which form mutual bonds and/or form bonds with other components of the formulation. For this it can, if appropriate, be necessary to add an initiator or a catalyst, and/or to supply energy, for example in the form of heat, UV radiation, or another form.

Examples of reactive components that can be used are hydroxy, mercapto, amino, carboxy, carbonyl, sulphonyl, epoxy, β-ketoester, isocyanate, and vinyl groups; isocyanates are preferred.

These can, if appropriate, also be present in protected form, e.g. the isocyanate group reacted with, for example, alcohols, with phenols, with oximes, with caprolactams, with amines or with C—H-acidic compounds.

The formulations have a wide field of application and can advantageously be used wherever the intention is to damp the vibration of a surface.

Examples of these applications in private households are the cladding of household devices, such as washing machines, refrigerators, kitchen machines and air-conditioning systems, and also the cladding of personal computers.

Examples in construction and engineering materials are pipes, floors and wallcoverings.

It is readily possible to conceive of a large number of other applications and application sectors. The surfaces to be coated can themselves be composed here of various materials, e.g. plastic, wood, ceramic, cardboard, or chip- and wood-fibre-based materials. Commonly encountered and particularly preferred surfaces are sheet metal surfaces.

Particular preference is given to the coating of bodywork parts in automobile construction. If the coatings are used externally in the underbody region and wheel-arch region of the motor vehicle, noise from impact of stones, sand and water is reduced, in addition to the damping of the vibrations of the sheet metal.

The same formulation can also be used to fill cavities, for example those occurring in automobile construction, for example in the roof struts or in A columns, in B columns and in C columns. Foamable formulations are often used for these applications. Alongside the damping of vibrations of sheet metal here, onset of vibration of any air columns included in these cavities is also prevented. 

1-26. (canceled)
 27. A plastisol formulation, comprising a) from 1 to 60% by weight of oligomers whose molar mass is smaller than 20 000 g/mol, and which contain at least 30% by weight of (meth)acrylates, b) from 0 to 60% by weight of solvents for the oligomers a), c) from 5 to 60% by weight of pulverulent polymers whose molar mass is greater than 100 000 g/mol, and d) other fillers, auxiliaries and/or additives, where components a) to c) make up at least 20% of said formulation.
 28. The plastisol formulation according to claim 27, wherein components a) to c) make up at least 40% by weight of said formulation.
 29. The plastisol formulation according to claim 27, wherein the oligomers a) contain at least 60% by weight of (meth)acrylates.
 30. The plastisol formulation according to claim 27, wherein the molar mass of each of the oligomers a) is <10 000 g/mol.
 31. The plastisol formulation according to claim 27, wherein the molar mass of each of the oligomers a) is <5000 g/mol.
 32. The plastisol formulation according to claim 27, wherein the oligomer or one of the oligomers contains free hydroxy, carboxy, or amide groups.
 33. The plastisol formulation according to claim 27, wherein a phthalate, adipate, phosphate or citrate is used as solvent b).
 34. The plastisol formulation according to claim 27, wherein a phthalate is used as solvent b).
 35. The plastisol formulation according to claim 27, wherein the molar mass of the polymers c) is >400 000 g/mol.
 36. The plastisol formulation according to claim 27, wherein at least one of the polymers c) is composed of more than 60% by weight of (meth)acrylates.
 37. The plastisol formulation according to claim 36, wherein each of the polymers c) is composed of more than 60% by weight of (meth)acrylates.
 38. The plastisol formulation according to claim 27, wherein at least one of the polymers c) is composed of more than 80% by weight of (meth)acrylates.
 39. The plastisol formulation according to claim 36, wherein at least one of the polymers c) is composed of more than 60% by weight of methyl methacrylate.
 40. The plastisol formulation according to claim 36, wherein at least one of the polymers c) is composed of more than 80% by weight of methyl methacrylate.
 41. The plastisol formulation according to claim 27, wherein the polymers c) take the form of particles whose size is from 200 to 1200 nm.
 42. The plastisol formulation according to claim 27, wherein the particles c) have a structure in which one or more shells is/are present with, optionally a different monomer constitution around a core.
 43. The plastisol formulation according to claim 27, wherein the oligomers a) and/or the polymers c) bear one or more functional groups which can result in post-crosslinking.
 44. The plastisol formulation according to claim 43, wherein said functional groups are hydroxy groups.
 45. The plastisol formulation according to claim 43, wherein post-crosslinking takes place via the addition of a reactive component.
 46. The plastisol formulation according to claim 45, wherein one of the reactive components is an isocyanate.
 47. The plastisol formulation according to claim 27, wherein the auxiliary, filler or additive d) is a blowing agent.
 48. A surface coating comprising the plastisol formulation according to claim
 27. 49. A sheet metal coating comprising the plastisol formulation according to claim
 27. 50. A coating for bodywork parts in automobile construction comprising the plastisol formulations according to claim
 27. 51. A composition for the damping of vibrations in sheet metal comprising the plastisol formulations according to claim
 27. 52. A composition for the filling of cavities comprising the plastisol formulations according to claim
 27. 